They look a lot like KC Daylighters. You might try one of their products.
On the other hand, I used metal light grills over my headlights for years on the Jeep, and still got broken headlights, but had a heck of a time keeping the lenses clean. I stopped using them long ago because they added little to the durability of the lights and were just a pain to maintain. If you are worried about them picking up a rock on the highway, keep them covered as you already do or turn them around so they point backwards. On the trail, the grid covers won't protect the lights to any appreciable degree.
